High-density polypropylene and polyethylene conduit are often laid underground in long lengths. Splices are required to join one length of conduit to the next. Fiber optic cables, or the like, are then installed in the length of conduit. Relatively smooth interior surfaces are required throughout the conduit length, including the splices, in order to facilitate the installation of the cable. The joints or splices need to be relatively airtight since air pressure is often used to install (blow) the cable through the conduit. Therefore, the coupling must provide a smooth interior surface and a relatively airtight joint.
A brochure from Cabletec®, with a title “Two-Piece PLASTIC REMOVABLE COUPLINGS:”, describes a series of different size couplings currently used in this field. The essence of Cabletec® part number PE1.900-2 is shown in FIG. 1. This prior art utilizes two half shells that are bolted together in such a way as to clamp the abutting ends of the conduits. Circumferential gripper rings in the half shells are utilized to bite into the conduit in order to resist axial separation forces. A seal is provided to prevent leakage in or out of the conduit joint. Tools are required to install the coupling.
U.S. Pat. No. 5,947,532 issued to Lorenz shows prior art of a “stab” type coupling. The conduit ends are inserted (“stabbed”) into a structure that contains a flexible collet. The collet is supported by an inclined surface in the structure in such a way as to permit insertion of the conduit into the structure, but prevents retraction. No tools are required for installation. However, after the conduit is inserted, it must be retracted some finite distance in order to activate the bite of the collet into the conduit. This is an obstacle in certain installations. Further, this coupling cannot be removed from the conduit without destroying the coupling or damaging the conduit.
U.S. Pat. Nos. 2,913,262 issued to De Cenzo et al, 4,008,937 issued to Filippi, 4,346,428 issued to Gale, and 5,380,052 issued to Hendrickson are all examples of couplings that utilize a toggle clamp to couple conduits. All of these examples require preparing the conduit ends with beads, threaded adaptors, grooves and the like. Therefore, the noted techniques would not be desirable or accepted in the field of the present invention.